Some heterogeneous wireless communication networks, for example, 3rd Generation Partnership Project (3GPP) Universal Mobile Telecommunications System (UMTS) Long Term Evolution (LTE) networks, comprise a macro cell-eNB (MeNB) and a home-eNB (HeNB) cell having overlapping bandwidth (BW) deployments that may subject user equipment (UE) to interference. Some HeNBs are closed subscriber groups (CSG) that serve only UE belonging to the Group.
Idle mode reselection behavior for LTE Release 8 (Rel-8) is specified in TS 36.304 v8.5.0. The existing reselection criterion for LTE Rel-8 uses reference signal received power (RSRP) from the serving cell as a mechanism to trigger reselection evaluation of neighboring base stations. This method is effective in recognizing when the UE moves out of a base station coverage area, but the RSRP will not trigger reselection evaluation when the UE is subject to interference from a neighboring base station, for example, when an idle mode UE camped on a MeNB is subject to interference from a neighboring HeNB.
FIG. 1 illustrates a first scenario wherein a UE camped on a MeNB is subject to interference from the HeNB when the UE is located near a HeNB. FIG. 2 illustrates another scenario wherein a UE camped on a HeNB is subject to interference from a MeNB that is located near the HeNB. Such interference may result in a missed page and the associated consequences (e.g., missed network-originated calls, etc.) by an idle mode UE.
R2-092416 entitled “Usage of IFRI with Cell Reselection to CSG cells” describes a mechanism wherein a UE camped on a MeNB attempts to reselect to a different carrier, i.e., performs inter-frequency reselection, upon detecting that an intra-frequency reselection indicator (IFRI) bit is set by a neighboring HeNB, wherein the set IFRI bit indicates that the HeNB and MeNB share a common carrier frequency. It has also been suggested that an idle mode UE camped on the MeNB “bar” the shared carrier frequency for a fixed duration (e.g., 300 sec) from reselection when the IFRI bit is set by the HeNB. In some systems, for example, LTE Release 9 (Rel-9), the SIB transmission must be decoded before the UE can determine whether the IFRI bit is set.
An alternate solution to interference in the scenario of FIG. 1 is to trigger inter-frequency reselection evaluation when the reference signal received quality (RSRQ) of the serving cell or base station falls below a threshold. This proposal however suffers from various drawbacks including, among others, lack of agreement on how to measure interference and the fact that the reliability of paging channel reception is dependent on various factors such as the transmit antenna configuration of the serving base station, the physical downlink control channel (PDCCH) code rate or aggregation level, frequency-dependent interference from the HeNB (eg., due to fractional frequency reuse), etc. resulting in a scenario that the RSRQ is not a good indicator of paging channel performance.
The RSRQ-based proposal although in principle can trigger macro cell UEs (MUEs) with potentially poor paging performance to start inter-frequency reselection evaluations, the RSRQ metric as it is defined in LTE Rel-8 will likely lead to a failure in fulfillment of this objective. The interference measurement used for estimating RSSI in the specification is not well defined (e.g., no specification on which RBs or subframes are used, whether RSRP should be narrowband or wideband, etc.) and as a result, different UE implementations might end up behaving differently. Further, even if all the UEs were to achieve consistency in interference measurement by a specification mandate, the fact that the reliability of paging channel reception is dependent on various factors such as the eNB transmit antenna configuration, PDCCH code rate or aggregation level, frequency-dependent interference from the HeNB (eg. due to fractional frequency reuse), etc. resulting in a scenario that RSRQ is not a good indicator of paging channel performance.
The various aspects, features and advantages of the disclosure will become more fully apparent to those having ordinary skill in the art upon careful consideration of the following Detailed Description thereof with the accompanying drawings described below. The drawings may have been simplified for clarity and are not necessarily drawn to scale.